Hydraulic props, particularly pit props



Dec. 12, 1961 H. F. HEINTZMANN ET Al.

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet1 mum/rags, 44W MM H W 3- Wk I Dec. 12, 1961 H. F. HEINTZMANN ETAI.

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet2 M W 5.2mm!

OAT -M;

Dec. 12, 1961 H. F. HEINTZMANN ETAL 3,012,545

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet3 PIC-i5 i llll Dec. 12, 1961 H. F. HEINTZMANN ETAL HYDRAULIC PROPS,PARTICULARLY PIT PROPS 4 Sheets-Sheet 4 Filed May 8, 1959 FIG. 6

IN VENfO/Pg H MW 1M Rum a Unite 3,012,546 HYDRAULIC PROPS, PARTICULARLYPH PROPS Hans Friedrich Heintzmaun, Rudolf Seiz, and Erwin Blenlile,Bochum, and Hellmut Lerhs, Hamburg-Langenhorn, Germany, assignors toBochumer Gesellschaft fiir Grubenaushau u. Technik m.b.H., Bochum,Germany, and Phoenix Gummiwerlre Aktiengesellschnft, Hamburg-Harburg,Germany Filed May 8, 1959, Scr. No. 811,827 Claims priority, applicationAustria May 10, 1958 14 Ciaims. (Cl. Ell-46) There are hydraulic props,and particularly pit props, having an inner prop member which is guidedfor axial displacement in an outer prop member, constituting acompression chamber, with a sealing means arranged between them. Furtherhydraulically-operating supporting devices and constructional apparatuscomprising a plurality of props, for example pillars, frames and walls,are known.

Water or oil, or a water-oil emulsion, are in these various instances,used as hydraulic media. The admission and discharge of the hydraulicmedium may, for example in a mining installation, be performed from asupply container common to a plurality of props and through connectingconduits disposed in a gallery, these conduits being connected tocouplings which are, for example, provided on the outer prop member. Itis also possible, however, to effect the admission and discharge of thepressure medium through the inner prop member. It is possible, moreover,that a separate supply container is associated with each prop, this forexample being disposed inside the inner prop member, and the pressuremedium is supplied from this container to the compression chamber formedby the outer prop member, during the extension of the prop parts, i.e.during the bracing of the prop between the roof and the floor.

In these known hydraulic props or supports, difficulty is met ineffecting the sealing between the telescopically interengaged propparts. In known forms of construction the sealing is almost exclusivelycarried out between the surfaces which are movable relatively to oneanother, and more particularly between a piston which is provided at theinner end of the inner prop member and the inner wall of the compressionchamber of the outer prop member.

To ensure adequate sealing, the sealing means must be fitted absolutelytight at these parts. The result of this, however, is that when the propis relieved of pressure, i.e. when an exhaust valve associated with thecompression chamber is opened, the inner prop is not inherently capableof sliding within the outer prop member on account of the largefrictional resistance set up by the inner member, and an additionalapplication and expenditure of eifort and work is required for thispurpose.

Fabrication of these known props is comparatively costly because thesealing surfaces require accurate machining. Moreover, the walls of theinner and outer prop members which constitute the sealing surfaces areexposed to considerable danger of corrosion and rusting, particularlywhen water is used as the pressure medium and, in view of theunavoidable mechanical stresses and strains applied to the prop parts inmining operations deformation and/or superficial damage of the sealingwalls of the prop readily occurs, and this may have the result that thecoupling between the inner and outer prop members becomes imperfectlysealed, and/or there may be jamming of the two telescopic prop members.

Such hydraulic props, support, pillars, frames, walls, or supportingstructures made up of pit props, of the kind referred to are generallyreferred to hereinafter as props,

' tion, by the fact that the inner prop member and the p and areimproved, in accordance with the present invenouter prop membersurrounding the same are interconnected by a fluidtight'bellows offlexible, for example resiliently deformable, material, which is guidedfor inversion and is adapted to perform a voluting movement on the innerand outer prop members during relative movement of these members. I

As a result, the connection between the two prop members is independentof any intersliding sealing surfaces, and consequently the frictionalforces which are developed during the relative shifting of the propmembers is reduced to a small proportion of the figure which is met within known prop constructions. Since there is no direct sealing betweenthe telescoping prop walls, it is possible to allow considerably greatermanufacturing tolerances than in known constructions. Moreover, anycorrosion and/or deformation of the prop walls is precluded fromimpairing the sealing of the prop members in any way whatsoever.

Advantageously the end sections of the volute bellows are firmly clampedto the inner and outer prop members, and it is generally found advisableto arrange for the clamping to take place at the outer wall of the innerprop member and the inner wall of the outer prop membet.

The volute bellows, firmly clamped atits ends and effecting the requiredsealing, rolls on the confronting surfaces of the inner and outerstructural parts, i.e. the inner and outer prop members, rolling off onesimultaneously with its being rolled out over the other, i.e. being bothinverted and performing a volute movement. For this purpose only asmall, and preferably resilient, deformation of the material of thebellows is required, and a correspondingly small expenditure of effort.

By virtue of the volute bellows which connects the two prop members infiuidtight fashion, the part of the prop or support disposed outside thecompression chambet is protected very effectively against corrosion.Furthermore, and particularly when water is used as the pres-. surefluid, the prop surfaces which are directly exposed to the pressurefluid can very easily be given a corrosionresisting protective coating,since these surfaces no long er have to fulfill the function of sealingsurfaces, in which case they would require very special and carefultreatment.

The tluidtight volute bellows is advantageously made of a suitableresilient material, for example being of natural or artificial rubber,one of the various kinds of plastics, or mixtures thereof, and isprovided with fabric inlays.

It is primarily of a construction such that the requisite rollingmovements, and the consequent variations in the diameter of the bellowscan be implemented without any difliculty. The bellows does not requireto be expansible in its longitudinal direction, or only to a smallextent. The degree of variation of the bellows diameter which isrequired during the volute movement is kept as small as possible. 'It isnot necessary for the bellows to conform exactly to the dimensions ofthe inner and outer prop members since the wall surfaces of the bellowsfacing the inner and outer prop members are applied by the pressure ofthe pressure fluid against these confronting walls.

In an advantageous embodiment, the clamping to the Advantageously aguide plate is attached to the inner j I end of the inner prop member,this being provided with perforations or peripheral recesses forconnecting the parts of the compression chamber, arranged at the twosides of the guide plate, for fluidflow between them. In this event, theend section of the volute bellows adjacent the inner prop member can beclamped between this guide plate and the end of the inner prop member.

In an advantageous arrangement the outer prop member comprises twocylindrical sections which are divided along a plane extendingsubstantially at right angles to the axis of the prop, and the endsection of the volute bellows adjacent the outer prop member is grippedbetween these cylindrical sections.

It is particularly advantageous in such an arrangement, for the twocylindrical sections of the outer prop member to be detachably coupledtogether by a coupling ring which encloses the adjacent ends of saidcylindrical sections in sleeve fashion externally and/ or internally.This enables the use of cylindrical sections for the outer prop memberwhich are of the same diameter at their adjacent ends. Use may thereforebe made of sections of tube which are to be come by in the tradewithout, for example, one end of the cylindrical section having to beenlarged and/or machined for the insertion or screwing in of the othercylindrical section. At the same time, any reduction in wall thicknessand in variation of the tensile strength in relation to the untouchedpart of the length of the cylindrical section is avoided. The use ofcylindrical or tubular sections which are readily available in the tradealso reduces the Overheads and costs of manufacture, without harming theetficiency of the prop.

in accordance with a further feature of the invention, the coupling ringhas a sealing flange which projects inwards in a substantially radialdirection and against which the adjacent ends of the two cylindricalsections seal. From this it will be immediately apparent that thesealing of the high pressure prop and the fluid therein is greatlysimplified and improved, since the sealing is not only performed by theannular surfaces of the coupling ring which bear against the outer andinner peripheries of the cylindrical sections of the prop, but also atthe end faces of the sealing flange.

A further improvement is secured by making the sealing flange ofsubstantial thickness in the longitudinal direction of the prop andhousing in this flange all the valves associated with the compressionchamber of the prop. This has the advantage that the valves are at apart of the prop, substantially in fact at about half the height of thelatter, outside the zone of movement of the inner prop piston, so thatthese valves can be arranged entirely within the prop withoutinterfering with the longitudinal shifting of the prop members. Apartfrom the fact that this guards the valves against damage (which is avery desirable condition in undergroundmining), this positioning of thevalves has the attribute that they are readily accessible formaintenance, when the prop is appropriately disposed, and are exposedonly to a very small degree to the liability of contamination or damageby coal, stone or rubble.

Generally speaking it is advantageous to arrange the valves in the samecross-sectional plane of the sealing flange offset from one another inthe peripheral direction, and such that the longitudinal axes thereofare radial in relation to the axis of the prop. As a result the width ofthe coupling ring, measured in the longitudinal direction of the prop,and the thickness of the sealing flange, can be comparatively small.

To prevent soiling of the valves, in accordance with a further featureof the invention the outwardly-directed connecting ports of the valvesare adapted to be closed against the ingress of dust. This can beeffected by pro viding for closure of the connecting ports by one ormore guard caps which is or are movably mounted on the coupling ring.Thus, for example, a guard cap having openings corresponding inpositions and diameter to the ports of the valves can be mounted on thecoupling ring so as to be movable thereon for the purpose of opening orclosing the valve ports. For this purpose the guard cap can be mountedon the coupling ring merely for rotary movement, or can be displaceablein the longitudinal direction of the prop. Additionally it is possibleto rotatably couple the guard cap with the coupling ring by means ofscrew threading which is pitched in the longitudinal direction of theprop. It can be arranged that when the guard cap is moved, either allthe valve ports are opened or closed simultaneously, or only certain ofthem at appropriate times. Furthermore a projection can be provided onthe guard cap to serve as a bearing for a lever for opening the pressurerelief valve.

The outer diameter of the inner prop member is advantageously made onlya little smaller than the inner diameter of the sealing flange of thecoupling ring which projects into the annular space between the outerprop member and the inner prop member. The virtue of this arrangement isthat the flow of the pressure fluid, and the volute movement of thebellows clamped at its ends to the outer and inner prop members, are notobstructed dur ing the setting or collapsing of the prop. The outermargin of the volute bellows is advantageously then clamped between thesealing flange of the coupling ring and the confronting end of the innercylindrical section of the outer prop member.

In accordance with a further feature of the invention, the marginalsections of the bellows clamped at the outer and inner prop members areof greater tensile strength than the remainder of the length of thebellows. This confers a greater resistance to the marginal sections ofthe bellows which are, naturally, exposed to heavier loads and stressesdue to their clamping to the prop members, and this increased resistanceensures a proper sealing of the compression chamber of the prop and aneflicient operation and life for the bellows.

To provide for this increased tensile strength relatively to the partsof the length of the bellows disposed between its ends, it is foundadvantageous to reinforce the marginal sections of the bellows bybeading. The stiffness hereby produced prevents the buckling in of thebellows at the ends under the effect of the fluid pressure whichprevails when the prop is loaded, whereby the marginal sections canadvantageously support the stresses which are required for sealing butnevertheless exhibit a degree of flexibility such as is required toallow the volute bellows to be laid into the prop, i.e. for a properoperation of the bellows.

The marginal sections of the volute bellows provided with beadingreinforcements may, in appropriate cases, be equipped with spacedsealing lips, the gaps between which provide for a stagewise sealing ofthe compression chamber.

The stiffness of the marginal sections of the volute bellows may befurther improved by providing the marginal beads with reinforcinginserts of materials of a greater tensile strength than that of theremainder of the bellows. These reinforcing inserts are advantageouslyin the form of stiffening rings which are embedded in the beads. Therings may, for example, be comprised of wire braid, wire cord or thelike and are advantageously prepared so as to provide for an effectivebonding between the same and the material of the bellows, which, forexample, is an elastomeric material such as natural or artificialrubber, plastics of various kinds, or mixtures of these. The stiffnessof the marginal sections of the volute bellows is so substantiallyincreased in this way as to practically preclude any danger of bucklingin of the margins.

Because the marginal sections of volute bellows is exposed to verypowerful stresses and strains, it is advisable to provide the bellowswith fabric inlays, at any rate in the marginal zones thereof. Inaddition the tensile strength of the bellows is considerably increasedby this means. Advantageously the fabric inlays are composed of at leasttwo superimposed corded layers embedded in the resilient material of thebellows. The corded fabric may be directly exposed to high tensilestrains and primarily fulfils the function of sustaining the tensilestresses which are developed in the bellows, and in view of the smallthickness of the fabric the bellows may be of smaller wall thickness.Asa consequence of this, moreover, when the bellows rolls on and offbetween the inner and outer prop members, only a small resistance tobending occurs and this promotes a substaintially extended length ofuseful life for the bellows.

The reduced wall thickness of the bellows, allowed for by using thecorded fabric, enables the radial distance between the inner and outerprop members to be kept comparatively small. in consequence of this avolute bellows of this nature can sustain relatively high specificsurface pressures. In this connection a further improvement is achievedby crossing the cord lengths at an angle of about l040 and disposingthem substantially symmetrically in relation to the longitudinal axis ofthe prop. Apart from the fact that the crossed arrangement of the fabricwebs promotes an unopposed volute movement of the bellows during theoperation of the prop, a bellows reinforced in this way is notablebecause of the limited expansibilit-y which it possesses, but at thesame time its capacity to sustain very high tensile strains. Inaddition, a crossover system of fabric webs very effectively opposestwisting forces acting on the bellows.

The capacity of the bellows to sustain powerful tensile strains can befurther increased by disposing the fabric inlays in sleeve fashionaround the reinforcing rings. By this means the portion of the volutebellows between its marginal sections is suspended by the fabric webs tosome extent on the reinforcing rings in the marginal beads of thebellows so that the forces which are more particularly effective at theclamped marginal beads are transmitted through the fabric to theremainder of the bellows. At the same time the fabric wrapping aroundthe reinforcing rings increases the cross-sectional size of the beadedmargin, thereby increasing the sealing properties. In addition theelasticity of the marginal beads is increased and the danger avoidedthat the resilient material of the bellows disposed above thereinforcing rings will be crushed and damaged under the action of theclamping forces.

A further feature of the invention resides in gripping the volutebellows in sealed fashion, directly alongside the marginal beads,between two clamping surfaces provided on the outer or the inner propmember, as the case may be. Advantageously the clamping surfaces areassociated with sealing surfaces which are applied against the marginalbead, whereby these beads are drawn, under the fluid pressure prevailingin the compression chamber of the prop, against the sealing surfaces ofthe clamping surfaces, and in the event of a high internal pressure inthe prop, are pressed under correspondingly high pressures against thesealing surfaces so as to effect complete sealing.

Advantageously the associated clamping surfaces are enlarged towards themarginal bead of the volute bellows to form an annular chamber which isof a crosssection which is only of slightly larger area than the beadedand reinforced margin of the volute bellows. As a result of this themarginal beads are exposed substantially only to the tensilestrains'which act on the bellows when the prop is under load, and aremounted freely in the annular chambers, depending on the size of theseforces and their elasticity; Since, as a-result, the parts of thebellows located in the vicinity of the heading are not subject at all,or only to an insignificant extent, to deformation, the anchorage andoverlapping of the fabric webs is safeguarded.

In this arrangement it is of advantage to associate with the clampingsurfaces centering and make-up surfaces which determine the minimumdistance between the 6. clamping surfaces. This can avoid damageoccurring as a result of an excessively powerful gripping of themarginal sections of the bellows. between the clamping surfaces can bemade dependent on the elastic properties of the material selected forthe bellows so that, in every case, the pre-tensioning efforts which arerequired for the clamping ensure, on the one hand, proper sealing and,on the other hand, ample conservation of the bellows material.

A further feature of the invention resides in the fact that the clampingsurfaces associated with the outer prop member are effective in thecross-sectional area of the outer prop wall and substantially parallelto the prop axis. Advantageously the clamping surfaces of the outer propmember are formed by the opposed ends of a clamping jaw and a couplingring which is detachably fastened to the outer cylindrical section ofthe outer prop member and is adapted to be clamped in the axialdirection to the clamping jaw by a clamping ring. The clamping ring isfreely rotatable on the clamping jaw of the inner cylindrical sectionbut is mounted for axial displacement towards the outer cylindricalsection of the outer prop member and is connected to the coupling ringby means of threading which is pitched in the axial direction.

This anchoring together of the two cylindrical sections of the outerprop member, which are preferably split in a plane at right angles tothe axis of the prop, reduces bending moments to a minimum, whilst atthe same time favorising the system of forces developed in the prop as aresult of the loading thereof. In addition the radial extent of theclamping surfaces, like the length of the volute bellows, can be keptrelatively small. The clamp ing ring not only allows for clamping of theouter margin of the bellows, but at the same time for the centeringtheannular gap between the inner and outer prop memhers is of a size asindicated, without being subject to damaging bending strains. A smallradial spacing between the inner and outer prop members additionallymeans that the outer prop member need not generally be of largerdiameter than conventional props which are not equipped with volutebellows.

It is also advantageous to telescope the outer and inner prop members insuch a way that only a small relative rotation is possible between thesetwo prop members during the telescopic movement. This makes the propmore efficient in operation and safeguards the bellows.

In one specific form, only the outer portion of the inner prop member iscylindrical, whilst the inner end of the inner prop member is formed bya guide plate which is connected to the cylindrical portion and isspaced from the latter, this guide plate being provided withperforations and being guided on the inner wall of the outer propmember. This substantially reduces the overall weight of the propwithout any impairing of the efiiciency or convenience in installation.The pressure fluid in the prop can flow to and from thecompressionchamber through the perforations in the guide plate,depending on the particular load conditions at any time. The guide plateon the inner prop member has the addi-. tional function that, like thecoupling ring of the outer propmember, it constitutes one of theabutments determining the fully extended length of the prop.

Advantageously the guide plate is detachably fastened The size of thegap to a threaded bolt which projects coaxially in relation to the propaxis into the compression chamber, the other end of this bolt beingfirmly, but detachably, connected to a plate for closing the cylindricalportion of the inner prop member, and a clamping plate, through whichpasses the threaded bolt, is adapted to be clamped against the closureplate by means of a nut screwed on to the threaded bolt.

Conveniently the end of the cylindrical portion of the inner prop memberis sealed by the closure plate, which conforms with the outer diameterof this inner prop member, and the side of this closure plate nearestthe compression chamber of the prop forms with the opposed side of theclamping plate an annular chamber for accommodating a marginal head ofthe volute bellows. This secures the same advantages as does the annularchamber which is provided in the outer prop member.

To enable the volute bellows to be applied with as little resistance aspossible from the clamping position on the inner prop member to theouter surface of this member, it is advantageous to give the clampingsurfaces on the closure plate a larger radius of curvature than theclamping surfaces on the clamping plate. As a result the clampingsurfaces of the clamping plate press the volute bellows more or less inthe direction of the superfices of the inner prop member, and thisbellows is therefore applied fully against the surface of this member.

In a further and advantageous embodiment of the invention, at least onefurther volute bellows is associated with the first-mentioned volutebellows, and the two bellows are coaxially nested and are in directcontact at least at the parts of their lengths adjacent the propmembers. This increases the load capacity of the prop, and consequentlyits safety in operation and its length of life, very considerably, sinceeach of the volute bellows has only to take a part of the total load.

The marginal sections of the volute bellows adjacent the prop members(outer and/or inner prop members) may be clamped in sealed fashion in acommon crosssectional plane of the prop or, in accordance with a furtherfeature of the invention, in different cross-sectional planes of theprop which are axially spaced from one another.

In an advantageous further arrangement, the volute bellows arecontinuously applied directly against one another over substantiallytheir full lengths, and the outer volute bellows, which is adjacent thecompression chamber of the prop and bears directly against the innerperipheral surface of the outer prop member and the outer peripheralsurface of the inner prop member, is of greater tensile strength thanthe inner volute bellows.

For the purpose of sustaining the pressure corresponding to a maximumloading of the prop, the outer volute bellows may be made of a materialof high tensile strength whilst the inner volute bellows is of amaterial which is adapted to seal the compression chamber of the prop.Since a larger radius of curvature is available for the outer volutebellows at the roll-over zone between the outer and inner prop members,than is available for the inner volute bellows, this outer bellows canbe of a harder and more robust, i.e. less flexible, material than theother bellows.

To avoid wear as a result of friction between the individual volutebellows, and at the same time to ensure a uniform transmission of thepressure effective in the compression chamber of the prop to the outervolute bellows, it is advantageous for the longitudinal sections of thevolute bellows of fluidtight material arranged in the vicinity of thevolute part of the bellows between the outer and inner prop members tobe spaced from one another in the longitudinal direction of prop and toenclose an annular chamber for receiving a fluid pressure transmittingmedium which is chemically neutral in relation to the material of thebellows.

Conveniently an admission conduit leading to the annular chamberaccommodating the pressure transmitting medium is provided between thevolute bellows in the vicinity of the position at which the marginalsections of the volute bellows are connected to the outer prop member.The relative movement between the outer and inner prop members isfacilitated by the pressure transmitting medium, which is advantageouslyincompressible and at the same time performs a lubricating function, andsticking together of the two volute bellows is avoided, even undermaximum load.

A number of embodiments of the invention are illustrated by way ofexample in the accompanying drawings in relation to pit props which areintended for use in underground mining.

In these drawings:

FIGURE 1 illustrates a first prop in longitudinal section;

FIGURE 2 is a cross section on the line IIII of FIGURE 1;

FIGURE 3 is a longitudinal section through a second embodiment of pitprop;

FIGURE 4 is a cross section on the line IV-IV of FIGURE 3;

FIGURE 5 is likewise a longitudinal section, in this case through athird embodiment;

FIGURE 6 is a longitudinal section through a fourth embodiment of theprop according to this invention.

In all the embodiments illustrated, the hydraulic pit prop, which ismore particularly intended for mining, comprises an inner prop member 1,which is here a lower prop member, and an outer and upper prop member 2.The outer and inner prop members are coupled together in fiuidtightfashion by at least one volute bellows 3. The inner margin of thebellows 3 is tightly and firmly clamped to the outer periphery of theinner prop member 1, and the outer margin of the bellows to the innerperiphery of outer prop member 2.

The outer member 2 comprises an inner cylindrical section 2a and anouter cylindrical section 2b, and in the embodiments illustrated inFIGURES I to 4, these two cylindrical sections 2a, 2b are connected by acoupling ring 4 which forms a sleeve surrounding the adjacent ends ofthe sections 2a, 2b at the exterior and is detachably connected to theseends, e.g. by screw threading 5. In contrast to the constructionsillustrated in FIGURES 1 to 4, the coupling ring can, of course, inappropriate cases, additionally surround the ends of the cylindricalsections 2a, 2b at the inside in sleeve fashion.

In all the embodiments illustrated in the drawings, the innercylindrical section 2a is of substantially shorter length than the outersection 2b, whilst both cylindrical sections are of the same internaland external diameters. It will be understood, however, that thediameter of the cylindrical sections 2a and 2b may be different, or theratio of their lengths may be other than that chosen in this particularcase.

As can be seen from FIGURES 1 to 4, the coupling ring 4 has a sealingflange 4a which projects radially inwards and against which theadjoining ends of the two cylindrical sections 2a, 2b are sealed, withan interposed packing 6 for the outer cylindrical section 2b and asealing ring 7 for the inner section 2a. The outer margin 3a of thevolute bellows 3 is gripped between the sealing flange 4a of thecoupling ring 4 and the end of the inner cylindrical section 2a of theouter prop member 2 opposed to this coupling ring, with a sealing ring 7disposed between them. As can be observed from FIGURES 1 and 3, theouter diameter of the inner prop member is less than the inner diameterof the sealing flange 4a which projects into the annular space 8 betweenthe outer prop member 2 and the inner prop member 1, but only by anamount corresponding to about four times the wall thickness of thebellows 3.

In the embodiment illustrated in FIGURES 1 and 2, the

sealing flange 4a of the coupling ring 4 is of a substantial thicknessin the longitudinal direction of the prop and one which exceeds itsradial width by a small amount. The sealing flange 4 houses an excesspressure valve 9 and a valve 10 disposed diametrically opposite it inthe same cross-sectional plane, this latter valve, which is of thenon-return type, being connected to a pressure medium supply conduit,and being at the same time adapted for use as a pressure relief valve.

It is, of course, possible to arrange more than two valves, offset fromone another in the peripheral direction, in the sealing flange 4a of thecoupling ring 4, for instance a non-return valve, an excess pressurevalve, and a separate pressure relief valve. The length of each of thevalve housings 9a, 10:: is approximately equal to the difference betweenthe inner and outer diameters of the coupling ring 4, so that the innerand outer surfaces of the coupling ring lie flush with the opposite endsof the valve housings 9a, 10a. This affords a minimum radial width forthe coupling ring 4.

To provide for a dust-sealed closure of the outer valve openings 9b, 1%of the respective valves 9, 10, a guard cap 11 is arranged on thecoupling ring 4, this cap surrounding the part of the coupling ring 4covering the cylindrical sections 2a, 2b and being rotatably mounted onthis ring. The guard cap is provided with openings 11a, 11b which are inpositions, and of a diameter, corresponding to the valve openings 91;,16b. Consequently the openings 11a, 11b are located in the samecross-sectional plane as the valve openings 9b, 10b, but are offsetdiametrically by 180 one relatively to the other. Thus a manual rotarymovement of the guard cap 11 can close or open both the valve opening ofthe non-return valve 9 and also that of the pressure relief valve 10.

It will also be understood that it is possible, instead of having arotatable mounting of the guard cap 11, to mount this so that it willslide on the coupling ring 4 exclusively in the longitudinal directionof the prop, in which event detent means or the like may be provided foradjusting or locking the position of the cap. Again, under certainconditions, the guard cap can be mounted for rotation on the couplingring 4 by means of screw threading.

A projection 12, fastened to the guard cap 11 in the vicinity of theopening 11b associated with the pressure relief valve 10, serves as abearing for a removable lever 13 for opening the pressure relief valve10. For this purpose, the lever 13 is in the form of a hinged leverwhose shorter lever arm can be pushed into the valve opening 10b of thepressure relief valve 10. When this occurs, the valve body is liftedfrom its seat against the pressure of a closure spring, so thatcompressed fluid can pass into the annular chamber 8 and, through aconnecting fluid conduit, to the compression chamber 8a.

The annular chamber 8 and the compression chamber 8a are separated by aguide plate 14 which is provided at the periphery with recesses 14a oflarge cross section to allow for a reciprocal flow of the pressure fluidbetween the compression chamber 8:: and the annular chamber 8. The guideplate 14 is secured to the inner end of the inner prop member by meansof a bolt 15 which is threaded so as to engage with a tapped bore in thebottom plate It; of the inner prop member 1, which bore is coaxial withthe prop.

The inner margin 3b of the volute bellows 3, which advantageously can beof beaded, reinforced construction, as can also the outer margin 3a, isgripped between the end surface of the inner prop member 1, which isconstituted by a section of tube, and a recess 14b in the guide plate 14in the form of an annular groove.

As can be seen from the drawing, the clamping efforts direction of thesuperfices of a cylinder of a diameter equal to the mean diameter of theouter prop member 2 and the inner prop member 1.

When the telescopic prop parts are extended, the bellows 3 rolls off theinner prop member 1 and a corresponding length of this bellows isapplied against the inner face of the outer prop member 2. When the propparts are telescoped in the opposite direction, contrarywise a part ofthe bellows 3 lifts off the inner wall of the outer prop member 1 and isrolled over and applied against the outer face of the inner prop member2, wherefore it has been termed a volute bellows.

The inner margin 31) of the volute bellows may, in contrast to thearrangements illustrated in FIGURES l to 4, be clamped or fastened tothe inner prop member 1 at a considerable distance from the guide plate14, and this allows for the use of a bellows 3 of a comparatively smallaxial length. The arrangement of the clamping zone at the inner end ofthe inner prop member 1 has, however, the advantage that the innermember is then undivided and exposed over its full length to the directaction of the pressure fluid. The part at which the outer margin 3a ofthe bellows 3 is clamped can, in contrast to the embodiments illustratedin the drawing, alternatively be provided directly in the vicinity ofthe head plate 17 of the outer prop member 1 so that the guide plate 14slides over the inside of the bellows. In this event the outer propmember 2 will be enveloped over its complete length by the bellows 3.

In the embodiment illustrated in FIGURES 3 and 4,

the head plate 17 accommodates an inlet valve 18 in the form of aspring-loaded non-return valve, and a further valve 19 which serves bothas an excess pressure valve and a manually operable pressure reliefvalve. Valves 18 and 1? communicate with the compression chamber 3a ofthe outer prop member 2 through channels 20.

In the embodiments illustrated in the drawings, the inner prop member 1serves as the lower prop member, and the outer member 2 as the upperprop member. This arrangement has the advantage that there is no needfor any special or careful caulking between the inner mem her 1 and acap 21 which closes the outer prop member 2 at its inner end. Nocontaminating bodies can be deposited at this part nor can any damageoccur here from fracturing stone. This arrangement conforms with thebasic principle of the invention, which is that only very minor sealingmeans, or if possible none at all, which are provided by surfaces whichslide relatively on one another, are used. The arrangement of the propillus trated in the drawings is not, however, essential to the operationof the bellows 3 provided in the prop, and the latter can therefore beinverted through without any undue diificulty so that the inner propmember 1 represents the upper prop and the member 2 the lower propmember bears against the ground.

It is also possible to combine a plurality of props of the formsdescribed above to form pillars, and fluid conduits may be so connectedbetween the compression chambers of the various props as to allow forbalancing the loading of the props. parts of a supporting member of avery large diameter so as to produce a supporting pillar in the form ofa single prop.

The marginal sections 3a, 3b of the bellows 3 which are fastened to theouter and inner prop members 2 and 1 respectively are to be of greatertensile strength than the remainder of the bellows and, for thispurpose, are thickened or beaded. The marginal beads of the bellows 3,which may be made of an elastomeric material, for example of natural orartificial rubber or of plastic with rubber-like properties, areprovided with rein-forcing inserts of material which is of greatertensile strength than the bellows 3 itself.

These reinforcing inserts may, for example, be constb tuted bystiffening rings 22, 23 which are embedded in the marginal beads 3a, 3band advantageously comprise It is also feasible to make the wire, cord,braid or the like. The stiffening rings 22, 23 advantageously aretreated, so as to be capable of firm bonding to the elastic material ofthe bellows 3, prior to being incorporated in the marginal sections. Inaddition, the bellows 3 is provided, at least in the vicinity of itsmarginal sections 3a, 3b, with woven inserts consisting of at least twocorded layers which are arranged one above the other and are embedded inthe elastic material of the bellows. These corded fabrics (which havenot been illustrated in the drawings) are advantageously crossed at anangle of about to 40 and are arranged substantially symmetrically inrelation to the longitudinal axis of the prop, the reinforcing rings 22,23 being surrounded sleevewise by the fabric inlays.

The volute bellows 3 is made of a length advantageously somewhat morethan half of the length of the full stroke of the prop so that, when theprop is in its unstressed condition, the bellows is relieved of stress,and where the prop is set the bellows is stressed exclusively by thefluid pressure prevailing in the compression chamber 8a and in theannular chamber 8.

It will be understood that material other than woven cord can be used asthe inlays of high tensile strength. Thus, for example, fabrics of metalor plastic materials can be used in appropriate circumstances, so longas they fulfill the condition that they are of high tensile strengthallied with a limited capacity for expansion.

In the embodiment illustrated in FIGURE 5, the marginal head 3a of thebellows 3 is arranged in an annular chamber 24 in the outer prop member2, which chamber is of larger diameter than the outside diameter of theprop member 2 and whose cross-section is slightly more than that of themarginal bead 3a. One half of the annular chamber 24 accommodating theouter marginal bead 3a is defined in a coupling ring 25, and the otherhalf by a clamping jaw 26, the coupling ring 25 being connected to theouter cylindrical section 2b of the outer prop memher 2, with aninterposed packing 27, by means of threading 28. On the other hand, theclamping jaw 26 is welded to the inner cylindrical section 2a of theouter prop member 2, and is thereby sealed. The opposed end surfaces ofthe coupling ring 25 and the clamping jaw 26, defining the annularchamber 24, are formed in the vicinity of the outwardly-directedperipheral portion of the annular chamber 24 as centering and make-upsurfaces 25a and 26a respectively, these parts serving to centre thecylindrical sections 2a, 2b of the outer prop member, which are split ina plane substantially at right angles to the prop axis, and to applythem firmly one against the other in the axial direction.

The clamping surfaces 25b, 26b, of the coupling ring 25 and the clampingjaw 26, which are flared outwardly to the annular chamber 24, are spacedby an amount determined by the mutually seating surfaces 250 and 26a andserve for the sealed gripping and fastening of the bellows 3 directlyadjacent the outer annular marginal bead 3a, for which purpose theclamping surfaces 25b, 2611 are provided with sealing surfaces whichbear against the bead.

The clamping faces 25b, 26b of the coupling ring 25 and the clamping jaw26 associated with the outer prop member 2 are effective in the regionof the outer prop wall and substantially parallel to the prop axis. Theclamping surfaces 25b, 2612, which are rounded, merge progressively intothe cylindrical inner surface of the coupling ring 25 and the clampingjaw 26 respectively, and the diameter of these parts is substantiallythat of the inner diameter of the outer prop member 2.

To develop the tightening effort which is required to clamp the annularbead 3a of the bellows 3 and to connect the two cylindrical sections 2a,2b of the outer prop member 2, use is made of a clamping ring 29 whichis freely rotatable on the clamping jaw 26, but is mounted so as to beaxially immovable towards the outer cylindrical section 212 of the outermember 2, and is connected to the coupling ring 25 by means of threadingwhich is pitched in the axial direction.

The coupling ring 25 has an annular flange 25c which is directedradially inwardly and has both the compression chamber 8a and theannular chamber 8 of the prop, connected to chamber 8a, both arrangedtherein. FIG- URE 5 only shows the spring-loaded excess pressure valve30 and this has a valve housing of a length substantially equal to theradial width of the flange 250. The inlet valve for the pressure fluid,which is in the form of a nonreturn valve, and the manually operablepressure relief valve, which are also arranged in the annular flange 25cof the coupling ring 25, are not shown in FIGURE 5.

The annular flange 250 has an inner diameter which correspondssubstantially to the mean diameter of the annular chamber 8. As a resultit is, of course possible to make the inner surface of the coupling ring25 flush with the inner wall of the outer prop member 2. On the otherhand it may, in other instances, be more advantageous to so provide thecoupling ring 25 that the end of the outer cylindrical section 2bencloses this ring in sleeve fashion not only externally, but internallyas well.

FIGURE 5 shows that the annular chamber 8 is made larger than the outerradius of the inner prop member 1 by an amount which is approximatelyfour times the wall thickness of the bellows 3. The inner prop member 1,and the outer prop member 2 are guided, one in the other (by means notshown) so that only a small relative rotation is possible between thesetwo members.

The inner marginal bead 3b of the bellows 3 is made of smaller diameterthan the outer diameter of the cylindrical part 1a of the inner propmember 1. The annular bead 3b is mounted in an annular chamber 31 at theinner end of the cylindrical part 1a which is of a crosssection alsolarger than the cross-section of the annular bead 3b.

The bellows 3 is provided externally, and in the vicinity of the innerannular bead 3b, with circular sealing lips 3c which are accommodated ina sealing surface 32c, which is recessed in annular groove fashion, of aclamping plate 32. The plane of the annular sealing surface 32c isapproximately at right angles to the longitudinal axis of the prop, andthis surface is of greater radial width than the annular chamber 31.

The sealing surface 32c of the clamping plate 32 is bounded externallyby a rounded rim which projects towards the inner prop member 1 andforms a clamping surface 32b which presses the part of the length of thebellows 3 directly adjacent the marginal bead 3b against the clampingsurface 33b of a closure plate 33 of the inner prop member 1.

The clamping surface 33b of the closure plate 33 is turned inwards,through an angle of about 45 relatively to the prop axis, towards thecompression chamber and constitutes the outer rim of an annular groovewhich is disposed below the same and forms the major part of the annularchamber 31. The clamping surface 331; provided on the closure plate 33is of greater radius of curvature than the clamping surface 32/; on theclamping plate 32, whereby the bellows 3 is pressed towards the outerend of the inner prop member 1 and against the outer surface of thelatter.

The opposed faces of the clamping plate 32 and the closure plate 33 ofthe inner prop member are provided with conforming centering and make-upsurfaces 321: and 33a, by means of which the clamping plate 32 iscentered on the closure plate 33 and is applied against the latter inthe axial direction. At the same time, this interseating of the surfaces32a, 33a determines the distance between the clamping surfaces 32b and33b of the clamping plate and closure plate, and this is so chosen, inaccordance with the wall thickness of the bellows 3, that there is areliable and effective clamping of the head 31) without damage to thebellows 3.

In the embodiment illustrated in FIGURE 5, with the object of securing avery short bellows 3 and at the same time a large relative shiftingmovement, the outer bead 3a is fastened approximately mid-way betweenthe two end positions of the inner bead 3b.

The closure plate 33 is screwed into the shorter cylindrical part 111 ofthe inner prop member by threading 34. It is provided at the end with athreaded bolt 35 which projects in the direction of the prop axis intothe annulus chamber 8, and a guide plate 36 is screwed on to the freeend of this bolt at a substantial distance from the inner end of thecylindrical part 1a.

The guide plate 36 is provided with a plurality of perforations 36a oflarge diameter. The pressure fluid can flow through the perforations26a, when the prop parts are extended, into the pressure chamber 8alocated between the guide plate 36 and the head plate 17 of the outerprop member 2, and when the prop parts are telescoped together, it canflow back through these perforations into the annular chamber 8. Theclamping plate 32 Slipped over the flanged bolt 35 is held by means of anut 37 against the closure plate 33 and the marginal bead 3b of thebellows.

As can be seen from FIGURE 5, the guide plate 36 of the inner propmember 1 and the coupling ring 25 of the outer prop member 2 constituteabutments which define the extended length of the prop, whilst thetelescopic zovement of the prop parts is limited by the abutment of theguide plate 36 of the inner prop member 1 against the head plate 17 ofthe outer prop member 2.

In the embodiment illustrated in FIGURE 6, the volute bellows connectingthe inner and outer prop members has associated therewith at least onefurther volute bellows 33, these two bellows 3 and 38 being nestedcoaxially in direct mutual contact, at least at the parts thereofadjacent the prop members 1 and 2.

The bellows 3, 38 are made of a fluidtight material, for example ofelastomeric materials, that is to say of synthetic rubbers orrubber-like plastics. The sections 30, 380 of the bellows 3, 38 locatedat the rolling zone between the outer and inner prop members areas seenin the longitudinal direction-spaced from one another and enclose anannular chamber 39 for receiving a pressure transmitting medium, forexample water, which is chemically neutral in relation to the materialof the bellows. The volume of the pressure transmitting medium, whichalso exerts something of a lubricating function between the bellows, issubstantially smaller than the volume of the operating medium in thecompression chamber 8a and the annular chamber '8 of the prop.

Generally speaking, it suffices if the axial distance between thelongitudinal'sections 3c, 380 between the outer and inner prop membersin the volute zone is substantially equal to the wall thickness of asingle bellows. The annular chamber 39 is so constituted that the outerand inner marginal sections 3a, 38a and 3b, 38b of the bellows 3, 38 aregripped at two different cross-sectional planes in the prop. In thepresent instance the axial distance between the clamping planes at theouter prop member is greater than those which apply at the inner propmember, and the two bellows are of the same length. t will be understoodthat the annular chamber 39 can be so formed that the bellows 3, 38 areof different lengths, presuming that the outer and inner marginalsections are gripped in a common plane.

When the prop is free of load, the pressure transmitting medium ischarged into the annular chamber 39, preferably With the prop members ina relative position such that the sections 30, 38c of the bellows in thezone of the voluting portions are at the level of a closable admissionconduit 45) which is provided between the clamping zones of the outermarginal sections 3a, 38a. In the normal operating condition, theadmission conduit 4! is covered by the inner bellows 38.

Whilst in the embodiment illustrated in FIGURE 6 the bellows 3, 38 areof the same elastomeric material and of the same wall thickness, andinclude a reinforcement of steel cording which may increase towards thecentre and consequently sustain in each case about half the pressureprevailing in the compression chamber of the prop, it will be understoodthat the outer bellows 3, may be of greatertensile strength than theinner bellows 38. To this end, either the wall thickness of the outerbellows 3 can be increased, or it may be made of a stronger material.

If the use of a pressure transmitting medium between the bellows 3, 38is dispensed with, these bellows may be applied directly against oneanother over substantially their full lengths, in the event that theouter bellows 3 is, for the purpose of sustaining a pressurecorresponding to the maximum prop loading, made of a material of hightensile strength, e.g. steel mesh or steel net, and the inner bellows isof a material, e.g. rubber, which is adapted to seal the compressionchamber of the prop in fluidtight fashion.

In the embodiment illustrated in FIGURE 6, the marginal sections 31),38b and 3a, 38a of the bellows 3, 38, which are fastened to the innerand outer prop members respectively, are of greater tensile strengththan the remainder of these bellows and for this purposehave areinforcing beading. The marginal beading is provided with reinforcinginserts of a material which is of higher tensile strength than thematerial of the bellows.

In the embodiment illustrated in FIGURE 6, reinforcing rings 22, 23 areembedded within the marginal beads 3a, 38a and 3b, 381), and these mayfor example be of wire braid, wire cords or the like. Before beingembedded, these reinforcing rings are advantageously prepared so thatthey will potentially bond very effectively to the resilient material ofthe bellows 3, 38.

In addition, the bellows 3, 38 may be provided, at any rate in the zonesof their marginal sections 3a, 3b and 38a, 38b, with fabric inlaysconsisting of at least two layers of cord arranged one above the otherand embedded in the elastic material of the bellows. The cord layers,which are not shown in FIGURE 6, may advantageously be crossed at anangle of about 10 to 40, and substantially symetnically to thelongitudinal axis of the prop, the reinforcing rings 22, 23, beingsurrounded sleevewise by the woven inserts.

The bellows 3, 38 are advantageously of a length equal to more than halfthe extending stroke of the prop, so that the bellows are relieved ofload when the prop is in its collapsed condition, and are loadedexclusively by the fluid pressure prevailing in the compression chamber8a, and the annular chamber 8, when the prop is set.

The gripping means for the outer annular beads 3a,

38a, which are arranged in axially spaced transverse planes, areconstituted by the opposing end faces of a clamping jaw 41, which issecured to the inner cylindrical secti n 2a of the outer prop member 2,and a coupling ring 43 which is connected thereto by a clamping'ring 42andis secured to the outer cylindrical section 2b of the outer propmember, and by at least one intermediate ring 44 which is providedbetween the coupling ring 43 and the clamping jaw 41. The opposed endfaces of the clamping jaw 41, of the intermediate ring 44, and thecoupling ring 43, in each case define an annular chamber to accommodatethe beads 3a, 38a of the two bellows, these annular chambers having adiameter which 'is larger than that of the outer prop member and acrosssectional area which is sli htly larger than that of the annularbeads 3a, 38a.

The end faces of the coupling ring 43, the intermediate ring 44, andtheclamping jaw 41, defining the annular chambers are in the form ofmake-up. pieces 45, 46 in the vicinity of the outwardly directedperipheral part of the annular chambers, and these pieces determine the:

axial distance between the cylindrical sections 2a, 2b.

at right angles to the axis of the prop.

The clamping surfaces of the coupling ring 43, the intermediate ring 44and the clamping jaw 41 which are flared outwardly towards the annularchamber, and are directed towards one another in bead fashion, arearranged at a distance from one another determined by the seating of thesurfaces 45, 46, and serve to sealingly grip the bellows 3, 38 directlyalongside the annular beads 3a, 38a.

The clamping surfaces, projecting in beaded fashion towards one another,for the outer marginal beads of the bellows are effective in the zone ofthe wall of the outer prop member 2, and substantially parallel to theaxis of the prop. The clamping surfaces, which are rounded off at theirends, merge progressively into the inner surfaces of the coupling ring43, the intermediate ring 44 and the clamping jaw 41, the diameter ofwhich corresponds substantially to the inner diameter of the upper propmember 2.

The clamping ring 42 which extends over the annular ring 44 is providedwith holes 47 at the level of the inlet conduit 40 for the pressuretransmitting medium, and the conduit 40 is accessible through theseholes, if desired even when the prop is in use.

The clamping jaw 41 is welded to the cylindrical section 2:: of theouter prop member, whilst the coupling ring 43 is detachably connectedby means of threading 49 to the outer cylindrical section 2b, with apacking 48 interposed between them.

The coupling ring 43 has an annular flange 43a which extendssubstantially radially inwards, and all the valves between the outer andinner prop members associated with the compression chamber 8a and thecylindrical annular chamber 8 connected thereto, are disposed in thisflange. The accompanying drawing only depicts the spring loaded excesspressure valve 50, and the housing of this valve is of a lengthapproximately equal to the radial width of the flange 43a. The springloaded inlet valve and the manually adjustable pressure relief valve arenot shown but are also mounted within the sealing flange 43a of thecoupling ring 43.

The inner surfaces of the coupling ring 43, in contrast with the FIGURE6 illustration, may run flush with the inner wall of the outer propmember 2. It is also possible to so construct the coupling ring 43 thatthe latter encloses the end of the outer cylindrical section 2]) insleeve fashion not only at the outer side, but also at the inner side.

FIGURE 6 shows that the radial width of the cylindrical annular chamber8 between the inner and outer prop members is about six times the wallthickness of the bellows 3 or the bellows 38. The inner prop member 1and the outer proper member 2 are guided one in the other by guide means(not shown) so that only a small amount of relative rotation is possiblebetween these prop members when there is a relative longitudinalshifting.

As can be seen from FIGURE 6, the surfaces by means of which the innermarginal beads 3b, 38b of the bellows, associated with the inner propmember 1, are clamped are constituted by the opposed end faces of aclosure plate arranged on the inner end of the cylindrical part 1a ofthe inner prop member, a clamping plate 54, and at least oneintermediate washer 55 provided between the closure and clamping plates.The clamping plate 54 is displaceable on a screw-threaded bolt 52, whichprojects from the closure plate 51 axially in relation to thecompression chamber 8a of the prop, and is adapted to be fastenedagainst this closure plate 51, or the interposed washer 55, by means ofa threaded nut 53.

The inner marginal beads 3b, 38b of the bellows are of smaller diameterthan the outer diameter of the cylindrical part 10 of the inner propmember, and the marginal bead 3b is mounted in an annular groove of theclosure plate 51, which is of larger cross-sectional area than themarginal bead 3b. The annular groove is bounded at the end by the washer55, which is of larger diameter than the closure plate 51, and has atits outer edge a rim 16 which projects in bead fashion from the closureplate and the clamping plate. The marginal bead 38b of the inner bellows38 is clamped towards the interior of the prop between the washer 55 andthe clamping plate 54, this latter plate being slightly smaller indiameter than the washer 55.

Mounted on the outer end of the screw bolt 52, which projects into thecompression chamber 8a of the prop, is a guide plate 36, similar to thearrangement illustrated in FIGURE 5, which is provided with perforations36a of large area. The medium for operating the prop can flow throughthese perforations 36a from the compression chamber 8a between the guideplate 36 and head plate 17 into the annular chamber 8 between the innerand outer prop members, and inversely.

As in the embodiments of FIGURES 1 to 4, the constructions illustratedin FIGURES S and 6 can, without any complexity, be used in a positioninverted through from that shown, so that the inner prop member 1 servesas the upper prop member, and the outer prop member 2 as the lower propmember.

We claim:

1. In a pit prop, in combination, an outer pit prop member and an innerpit prop member extending only partly into said outer pit prop member,said members being coaxial and said inner pit prop member having at alltimes a portion extending outwardly beyond said outer pit prop member,the exterior diameter of said inner pit prop member being substantiallyless than the inner diameter of said outer pit prop member so that saidmembers define between themselves an annular axially extending space;means carried by one of said members and slidably engaging the other ofsaid members for guiding said members for movement telescopically withrespect to each other along their common axis; and an elongated,fluid-tight, flexible sleeve located in said space and having a pair ofopposed ends respectively connected fluid-tightly to said members, saidsleeve, during telescopic movement of said members with respect to eachother along their common axis, rolling between the inner surface of saidouter member and outer surface of said inner member, and said sleevedefining in said outer member a compression chamber located on one sideof said sleeve for receiving a fluid which will produce the telescopicmovement of said members, whereby the area of sliding contact betweensaid means carried by said one member and slidably engaging the othermember can be reduced to a minimum and need not be relied upon forfluidtightness.

2. in a pit prop, in combination, an outer pit prop member and an innerpit prop member extending only partly into said outer pit prop member,said members being coaxial and said inner pit prop member having at alltimes a portion extending outwardly beyond said outer pit prop member,the exterior diameter of said inner pit prop member being substantiallyless than the inner diameter of said outer pit prop member so that saidmembers define between themselves an annular axially extending space;means carried by one of said members and slidably engaging the other ofsaid members for guiding said members for movement telescopically withrespect to each other along their common axis; and an elongated,fluid-tight, flexible sleeve located in said space and having a pair ofopposed ends respectively connected fluidtightly to said members, saidsleeve, during telescopic movement of said members with respect to eachother along their common axis, rolling between the inner surface of saidouter member and outer surface of said inner member, and said sleevedefining in said outer member a compression chamber located on one sideof said sleeve for receiving a fluid which will produce the telescopicmovement of said members, whereby the area of sliding contact betweensaid means carried by said one member and siidably engaging the othermember can be reduced to a minimum and need not be relied upon forfluidtightness, the length of said sleeve being at least equal to themaximum stroke of said members during telescopic movement thereof onewith respect to the other.

3. In a pit prop, in combination, an outer pit prop member and an innerpit prop member extending only partly into said outer pit prop member,said members being coaxial and said inner pit prop member having at alltimes a portion extending outwardly beyond said outer pit prop member,the exterior diameter of said inner pit prop member being substantiallyless than the inner diameter of said outer pit prop member so that saidmembers define between themselves an annular axially extending space;means carried by one of said members and slidably engaging the other ofsaid members for guiding said members for movement telescopically withrespect to each other along their common axis; and an elongated,fluid-tight, flexible sleeve located in said space and having a pair ofopposed ends respectively connected fluid-tightly to said members, saidsleeve during telescopic movement of said members with respect to eachother along their common axis, rolling between the inner surface of saidouter member and outer surface of said inner member, and said sleevedefim'ng in sa'd outer member a compression chamber located on one sideof said sleeve for receiving a fluid which will produce the telescopicmovement of said members, whereby the area of sliding contact betweensaid means carried by said one member and slidably engaging the othermember can be reduced to a minimum and need not be relied upon forfluid-tightness, said sleeve being fixed to said inner member at the endthereof which is located within said outer member and said sleeve beingfixed to said outer member at a portion thereof which is spacedsubstantially from the end of said outer member which surrounds saidinner member.

4. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only in part into said outer memberand having at all times a portion extending beyond said outer member,said outer member having a closed end located at all times beyond saidinner member and an opposed annularend surrounding said inner member,the outer diameter of said inner member being substantially smaller thanthe inner diameter of said outer member so that the portion of saidinner member which extends into said outer member defines with thelatter an elongated annular space; a guide plate located within saidouter member slidably engaging the inner surface thereof and locatedbetween said closed end of said outer member and the end of said innermember which is directed toward said closed end of said outer member andlocated within said outer member, said plate being formed with cutoutspassing therethrough; connecting means connecting said plate to saidinner member so as to be immovable with respect thereto; and anelongated, flexible, fluid-tight .sleeve located in said annular spaceand respectively having opposed ends fixed fluid-tightly to saidmembers, said sleeve defining a compression chamber between said sleeveand said closed end of said outer member.

5. In a pit' prop, in combination, inner andouter coaxial pit propmembers, said inner member extending only in part into said outer memberand having at all times a portion extending beyond said outer member,said outer member having a closed end located at all times beyond saidinner member and an opposed annular end surrounding said inner member,the outer diameter of said inner member being substantially smaller thanthe inner diameter of said outer member sothat the portion of said innermember which extends into said outer member defines with the latter anelongated annular space; a guide plate located within said outer member.slidably engaging the inner surface thereof and located between saidclosed end of said outer'member and the end of said inner member whichis directed towithin said outer member, said plate being formed withcutouts passing therethrough; connecting means connecting said plate tosaid inner member so as to be immovable with respect thereto; and anelongated, flexible fluid-tight sleeve located in said annular space andrespectively having opposed ends fixed fluid-tightly to said members,said sleeve defining a compression chamber between said sleeve and saidclosed end of said outer member, one end of said sleeve being fixed tosaid inner member between the end thereof which is directed toward saidclosed end of said outer member and said guide plate and the other endof said sleeve being fixed to said outer member at a portion thereofspaced substantially from said annular end of said outer member whichsurrounds said inner member, and said sleeve rolling between the outersurface of said inner member and the inner surface of said outer memberduring telescopic movement of said members one with respect to theother.

6. In a pit prop as recited in claim 1, said outer member including apair of tubular sections axially spaced from each other but locatedclosely adjacent to each other and annular coupling means coupling saidsections to each other, said coupling means clamping an end of saidflexible sleeve to one of said tubular sections.

7. In a pit prop as recited in claim 1, said outer mem ber including apair of tubular sections axially spaced from each other but locatedclosely adjacent to each other and annular coupling means coupling saidsections to each other, said coupling means clamping an end of saidflexible sleeve to one of said tubular sections, said coupling meanshaving an annular flange extending radially between said tubularsectionstoward' the 7 common axis of saidmembers and sealing meansproviding a fluid-tight seal between the ends of said sections and saidflange.

8. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only in part into said outer memberand havmg at all times a portion extending beyond said outer member,.

said outer member having a closed end located beyond said inner memberand an opposed annular end surrounding said inner member, said innermember having an exterior diameter substantially smaller than theinterior diameter of said outer member so that the portion of said innermember which extends into said outer member defines with the latter anelongated annular space, said outer member being composed of a pair oftubular sections slightly spaced axially one from the other; meanscarried by one of said members and slidably engaging the other ofsaidmembers for guiding said members for telescopic movement one withrespect to'the other along.

their common axis; an elongated flexible fluid-tight sleeve located insaid space, fluid-tightly fixed at oneend to the same to each other andclamping the end of said sleeve which extends between said sections toone of said sections in a fluid-tight manner, said coupling means"having an inwardly directed annular flange extending between saidmembers and said sleeve defining with said closed end of said outermember a compression chamber which communicates with said flange; andvalve means carried by said flange for participating in the control offluid to and from said chamber.

9. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only in part into said outer memberand having at all times a portion extending beyond said outer member,said outer member having a closed end located beyond said inner memberand an opposed annular end surrounding said inner member, said innermember having an ex terio'r diameter substantially smaller than theinterior diameter of said outer member so that the portion of said innermember which extends into said outer member defines with the latter anelongated annular space, said outer member being composed of a pair oftubular sections slightly spaced axially one from the other means;carried by one of said members and slidably engaging the other of saidmembers for guiding said members for telescopic movement one withrespect to the otheralong their common axis; an elongated flexiblefluid-tight sleeve located in said space, fluid-tightly fixed at one endto said inner member, and having an opposed end located between saidsection of said outer member; annular coupling means connected with saidsections for connecting the same to each other and clamping the end ofsaid sleeve which extends between said sections to one of said sectionsin a fluid-tight manner, said coupling means having an inwardly directedannular flange extending between said members and said sleeve definingwith said closed end of said outer member a compression chamber whichcommunicates with said flange; and valve means carried by said flangefor participating in the control of fluid to and from said chamber, saidvalve means including a plurality of valves each having an axisextending radially with respect to the common axis of said members andsaid valves being circumferentially distributed about the common axis ofsaid members.

10. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only in part into said outer memberand having at all times a portion extending beyond said outer member,said outer member having a closed end located beyond said inner memberand an opposed annular end surrounding said inner member, said innermember having an exterior diameter substantially smaller than theinterior diameter of said outer member so that the portion of said innermember which extends into said outer member defines with the latter anelongated annular space, said outer member being composed of a pair oftubular sections slightly spaced axially one from the other; meanscarried by one of said members and slidably engaging the other of saidmembers for guiding said members for telescopic movement one withrespect to the other along their common axis; an elongated flexiblefluid-tight sleeve located in said space, fluid-tightly fixed at one endto said inner member, and having an opposed end located between saidsection of said outer member; annular coupling means connected with saidsections for connecting the same to each other and clamping the end ofsaid sleeve which extends between said sections to one of said sectionsin a fluid-tight manner, said coupling means having an inwardly directedannular flange extending between said members and said sleeve definingwith said closed end of said outer member a compression chamber whichcommunicates with said flange; valve means carried by said flange forparticipating in the control of fluid to and from said chamber; andmeans carried by said coupling means for covering said valve means toprotect the latter from dust and other foreign matter.

11. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only in part into said outer memberand having at all times a portion extending beyond said outer member,said outer member having a closed end located beyond said inner memberand an opposed annular end surrounding said inner member, the exteriordiameter of said inner member being substantially smaller than theinterior diameter of said outer member so that the portion of said innermember which is located within said outer member defines with the latteran elongated annular space, each of said members having a pair ofclamping rings which define between themselves an annular chamber ofpredetermined cross sectional area and said rings having a pair ofcurved edges respectively directed toward each other and defining amouth of reduced cross section through which said annular chambercommunicates with said space; and an elongated flexible fluid-tightsleeve located in said space and having a pair of opposed enlargedannular ends respectively located in said annular chambers, the ends ofsaid sleeve respectively being of a smaller cross sectional area thansaid chambers and said curved edges of said rings clamping said sleeveat portions thereof closely adjacent to said enlarged end portions, thedistance between each pair of rings at said mouth thereof being smallerthan the thickness of the enlarged end portion of the ring so that saidclamping rings fluid-tightly clamp said sleeve to said members adjacentthe ends of said sleeve; and guide means carried by one of said membersand slidably engaging the other of said members for guiding said membersfor telescopic axial movement one with respect to the other.

12. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending at all times only in part into saidouter member so that said inner member has at all times a portionextending beyond said outer member and said outer member having a closedend located beyond said inner member and an opposed annular endsurrounding said inner member, said inner member having an exteriordiameter substantially smaller than the interior diameter of said outermember so that the portion of said inner member which is located withinsaid outer member defines with the latter an elongated annular space;guide means carried by one of said members and slidably engaging theother of said members for guiding said members for telescopic axialmovement one with respect to the other; and an elongated flexiblefluid-tight sleeve located in said space and having opposed endsrespectively fixed fluid-tightly to said members, said sleeve definingwith said closed end of said outer member a compression chamber adaptedto receive a fluid under pressure for telescopically moving said membersone with respect to the other, the radial thickness of said space beingapproximately equal to four times the thickness of said sleeve.

13. In a pit prop, in combination, inner and outer pit prop memberscoaxial with each other, said inner member extending only in part intosaid outer member and having at all times a portion extending beyondsaid outer member and said outer member having a closed end locatedbeyond said inner member and an opposed annular end surrounding saidinner member, the exterior diameter of said inner member beingsubstantially smaller than the interior diameter of said outer member sothat the portion of said inner member which extends along the interiorof said outer member defines with the latter an elongated annular space;guide means carried by one of said members and slidably engaging theother of said members to guide said members for telescopic axialmovement one with respect to the other; and a pair of flexible sleeveslocated next to each other in said space and each having opposed endsfluid-tightly connected with said members, one of said sleeves beinglocated nearer to said closed end of said outer member than the othersleeve and defining .a compression chamber therewith, and at least saidone sleeve being fluid-tight.

14. In a pit prop, in combination, inner and outer coaxial pit propmembers, said inner member extending only at a portion thereof into saidouter member and having at all times a portion extending beyond saidouter member and said outer member having a closed end located beyondsaid inner member and an opposed annular end surrounding said innermember, said inner memher having an exterior diameter substantiallysmaller than the interior diameter of said outer member so that theportion of said inner member which extends along the interior of saidouter member defines with the latter an elongated annular space, saidouter member being composed of a pair of tubular sections axially spacedslightly from each other; annular coupling means coupling said sectionsto each other and including an inwardly directed flange extendingradially between said sections beyond the inner surface of said outermember into said space; a guide plate formed with cutouts passingtherethrough and located 21 within said outer member between said closedend thereof and said inner member in slidable engagement with the innersurface of said outer member; connecting means connecting said guideplate to said inner member so as to be immovable with respect thereto,said flange cooperating with said plate to limit the telescopic movementof said members one with respect to the other in one direction; and anelongated flexible fluid-tight sleeve located in said space, having oneend fluid-tightly connected with said inner member, and having anopposed end fluid-tightly connected to said outer member between saidflange of said coupling means and the section of said outer member whichis most distant from said closed end thereof, said sleeve defining acompression chamber with the interior of said outer member at the sideof said sleeve between 15 2 949 395 22 the latter and said closed end ofsaid outer pit prop member.

References Cited in the file of this patent UNITED STATES PATENTS1,038,636 Oxnard Sept. 17, 1912 1,039,157 Mackintosh Sept. 24, 19121,492,158 Caretta Apr. 29, 1924 1,508,654 Hales Sept. 16, 1924 1,928,368Coffey Sept. 26, 1933 2,671,470 Boteler Mar. 9, 1954 2,673,573 FawickMar. 30, 1954 2,895,494 Adelson July 21, 1959 2,914,089 Allinquant Nov.24, 1959 Reuter Aug. 23, 1960

